Electrooptical translation system



Oct. 27, 1931. c. H. w. NASON ILICTROOPTIGAL TRANSLATION SYSTEM Filed Feb. 10 9:50

INVENTOR QM Q) me By H r 8 ATTORNEY Patented Oct. 27, 1931 UNITED STATES PATENT OFFICE CHARLES E. w. NABON, NEW YORK, N. Y., ASSIGNOE TO JENKINS TELEVISION GOE- POBATION, OF JERSEY CITY, NEW JERSEY, A CORPORATION OI DELAWARE ELEOTBOOPTICAL TRANSLATION SYSTEM Application filed February 10, 1980. 'Sertal No. 487,878.

This invention relates to electro-optical systems, and with particularit to methods and means for translating lig t variations into electric signals.

. by variations in photo-electric response having quasi-capacitance effect.

A feature of the invention relates to a method of analyzing and translating the shade characteristics of an object, image or visual representation into corresponding electric currents.

Another feature of the invention relates to a novel method of employing photo-electric variations to control-the resonance characteristic of an oscillatory circuit supplied from a source of carrier current. As a result of this latter feature the frequency spectrum of the transmitted carrier waves is substantially independent of the frequency variations of the light impulses incident upon the light sensitive device.

Other features and advantages not specifically enumerated will be apparent after a consideration of the followlng description and the appended claims.

In the drawings, Fig. 1 shows one preferred maimer of utilizing photo-electric variations to control the resonance characteristics of a transmission circuit;

Fig. 2 shows schematically how the amplitude of a carrier wave is varied according to the invention.

While the invention will be described in connection with a television system it will be understood that the novel features are capable of use in any system requiring electrooptical translation such as icture transmission, telegraphy, sound an other recording systems. Furthermore, while the inventlon is shown as embodied in a television system employing one particular form and arran 1 merit of apparatus, it will be understood tl st the nvention is not limited thereto. Accordmgly the numeral 1 represents a well known type of television scanning device in the form of a disc having a series of erforations or scanning elements therein. hen the ob]ect to be scanned is a continuously moving film or the like, as indicated in the drawing by the numeral 2, then these scanning perforations are arranged at equal radial distances from the axis of rotation of member 1. If desired these scanning elements may be arranged in spiral sequence as disclosed in U. S. Patent N 0. 1,679,086 to C. F. Jenkins. However, it is preferred to employ an arrangement such as disclosed in the copending application of C. H. W. Nason, Serial N 0. 418,205, filed January 3, 1930. Positioned on one side of disc 1, which is rotated at .the requisite speed from any suitable motive source (not shown), is a source of light 3, preferably of high and constant intensity such as an arc lamp. By means of a suitable optical system, represented schematically by numeral 4, the light from source 3 is projected. on the scanning disc 1. Consequently as the disc is rotated the film 21s illuminated in successive parallel strips across the width of the film. The light passing through each elemental area of the film is projected upon the photo-electric cell, preferably of the Elster-Geitel type, comprising a light-sensitive electrode or coating 6, and another electrode 7. It has been found by actual measurement that the electro-static capacity of such a cell undergoes variations in value as the coating is subjected to different degrees of illumination.

The electrodes of cell 5 are connected across an inductance 8 to form therewith an oscillatory circuit. This oscillatory circuit is preferably designed to have a relatively sharp resonance curve at the frequency of the carrier from source 9. For this purpose the inductance 8 may constitute the secondary of a high frequency transformer the primary of which is coupled to the carrier source 9. If desired the oscillatory circuit may include a condenser 10 to supplement the electro-static capacity of the cel 5.

Referring to Fig. 2 there is shown diagrammatically in curve A the resonance characteristic of the circuit includin the photocell 5 and the inductance 8. [he abscissae in Fig. 2 represent values of capacity, while the ordinates represent percentage resonance or amplitude of the carrier flowing in the tuned circuit. In order that there may be a proper and uniform relation between the amount of light incident upon the cell 5 and the amplitude of the carrier, it is preferred to design the constants of the oscillatory or tuned circuit so that the variations in capacity due to the cell 5, cause the amplitude of the carrier 0t vary between the points a b of the resonance curve or any other linear portion of said curve. In other Words the values of capacity and inductance in the tuned circuit are preferably so designed that when the maximum light falls on cell 5 the capacity of the tuned circuit has the value C, and when the cell is dark the capacity of the tuned circuit has the value d, consequently the amplitude of the carrier will vary as indicated by the curve B, and these variations in amplitude will correspond to the variations in shade of the elemental areas of film 2.

These varying carrier waves may then be impressed upon a broadly tuned radio-frequency amplifier of any well known type as indicated by the numeral 11. This amplified carrier having amplitude variations corresponding to the shade characteristics of film 1, may be transmitted by any suitable rad o transmission apparatus or system. If it IS desired to obtain a current corresponding to the amplitude variations merely, then the modulated carrier after being amplified by device 11, may be detected or demodulated by any well known demodulating device 1ndicated by numeral 13, this demodulator being tuned by the condenser 14 to the frequency of the carrier source 9. Th1s demodulated signal may be further amplified by device-15 and may be transmitted by any suitable transmission system, or it maybe employed to operate a suitable reproducing device such as a glow discharge lamp at a receiving station. In this latter case the reproducing lamp will, of course, be provided with an integrating scanner similar to the scaililner 1, and rotated in synchronism therewit lVhile the invention has been described in connection with certain specific apparatus and systems, it will be understood that the idea of utilizing the variations in capacitance of a photo-cell to control a tuned circuit or other similar capacitance responsive arrangement is capable of use in many other systems than that specifically disclosed.

\Vhile the above description premised on the variation in what has been termed elecclaims is intended to cover that variation in a photo-electric cell which appears to correspond to electro-static variations.

What is claimed is:

1. The method of signalling employing a carrier current which comprises translating the signals into corresponding light variations, varying the capacitance of a photoelectric cell in accordance with said light variations, and employing said capacitance variations to control the resonance of an ()scillatory circuit sharply tuned to resonance at the carrier frequency.

2. The method of signalling employing a carrier wave which comprises trai'islating the signals into variations in capacitance of a photo-sensitive device, and employing said variations to control tuning of a circuit sharply tuned to resonance at the carrier frequency.

3. The method of signalling which comprises translating the signals into photocapacitance variations, impressing carrier waves on a tunable circuit normally tuned to sharp resonance at the carrier frequency, and using said variations to control the tuning of said circuit.

4. The method of transmitting image characteristics which comprises producing light impulses corresponding to elemental areas of the image to be transmitted, impressing carrier waves on an oscillatory circuit sharply tuned to resonance at the carrier frequency, translating said light impulses into photocapacitance variations, and employing said photo-capacitance variations to control the tuning of said oscillatory circuit.

' 5. In a signalling system employing a carrier Wave the combination of a source of light variations, means for translating said variations into photo-capacitance variations. and a tuned circuit controlled by said photocapacitance variations, said circuit being sharply tuned to resonance at the carrier frequency.

6. In a signalling system the combination of a source of light variations, means for translating said variations into photocapacitance variations, a source of carrier current, and means including said translating means and a circuit sharply tuned to resonance at the carrier frequency for vary in the amplitude of said current.

I. In a'signalling system the combination of a source of carrier waves, a tuned circuit sharply tuned to resonance at the carrier frequency upon which said waves are impressed, and a variable capacity connected across said tuned circuit, said capacity bein light controlled.

8. n a signalling system the combination of a source of carrier waves, an amplifier device, a tuned circuit between said source and said device and sharply tuned to resonance at the carrier frequency, a variable photocapacitance connected across said tuned circuit, and a source of light signals for controllin said photo-capacitance. 9. T 8 method of signalling which comprises impressing carrier waves on a tuned circuit sharply tuned to resonance at the carrier frequenc and employing a photosensitive cell to (11mm said circuit in accordance with signals to be transmitted.

10. The method according to claim 9 in which said circuit is tuned to the frequency of said carrier waves.

- 11. In a television sg'stem employing a carrier wave, means or translating the shade characteristics of elemental areas of an image to be transmitted into corresponding lig t impulses, a photo-sensitive cell adaptedv to have its capacitance varied by said light impulses, a tuned circuit sharply tuned to resonance at the carrier frequenc a source of carrier waves impressed on said circuit and means including said photosensitive cell for detuning said circuit to control the amplitude of the carrier waves impressed thereon.

12. In atelevision system employmg a carrier wave, the combination of a scanning device, a photo-electric cell adapted to have its capacitance varied under control of said device, a tuned circuit sharply tuned to resonance at the carrier fre uency and adapted to be detuned by said p oto-electric cell to control the amplitude of a carrier wave, and means for amplifying the waves passed by said detuned circuit.

13. A system according to claim 12 in which means are provided for demodulatin the modulated carrier waves passed by sai tuned circuit and a light source controlled is: y by said demodulated waves.

In testimon whereof I have hereunto set my hand on t is 31st day of January, A. D.

CHARLES H. W. NASON. 

